Even as he prepares for a Saturday rally that could cement his status as an unparalleled force in conservative politics, Glenn Beck is facing quiet but persistent questions from some on the right about whether he can be a reliable partner for advancing conservative causes — or whether his main cause is advancing Glenn Beck.

Beck, the fiery talker who has emerged as a champion of the conservative populist tea party movement, predicted the rally — dubbed “Restoring Honor” — will be a historic “pivot point” that will re-center American public life around its founding principles.

Liberals, meanwhile, have blasted the event, as a partisan political rally intended to boost Republicans headed into the critical 2010 midterm elections. They’ve also accused Beck of exploiting civil rights iconography to advance his cause. Beck’s rally is scheduled to occur 47 years to the day after Martin Luther King delivered his “I Have a Dream Speech,” on nearly the same spot at the Lincoln Memorial where King spoke.

The rally will be keynoted by prospective 2012 GOP presidential candidate Sarah Palin and is being supported by a host of influential conservative groups and politicians, some of whom are planning political events before and after the rally. But Beck has insisted “Restoring Honor” is apolitical, casting it as a celebration of America’s military personnel by emphasizing that any proceeds will go to the veteran’s charity that is funding it and urging his followers to leave political signs at home.

Beck has received financial and promotional assistance for the rally from the National Rifle Association, Sen. Orrin Hatch (R-Utah), Rep. Jason Chaffetz (R-Utah) and leading tea party groups such as FreedomWorks, Tea Party Patriots and Americans for Prosperity.

“We very much appreciate and support Glenn’s general message that he puts forth on a daily basis. ... He consistently espouses free market views and views that espouse what the founders thought,” said AFP President Tim Phillips. “It’s a good message — and so whatever direction he chooses to take with this day and this march, we support it.”

But some conservatives — and even some Beck fans — say they’re concerned with what they view as a series of unfulfilled promises by Beck to engage more directly in the populist conservative politics he espouses on his syndicated radio show and Fox News television program. They point to his decisions to step away from a political group he founded, The 9.12 Project, and also to abandon plans for voter registration efforts and a political manifesto that was to have been launched at Saturday’s rally.

Beck declined to comment for this story through a spokesman.

Influential conservative blogger Erick Erickson said Beck won’t be able to answer what Erickson has called lingering questions about “whether he’s doing it for himself or doing it for the movement,” even with a successful event this weekend.

“People are going to want to see what comes out of this weekend long term — is it a flash in the pan or is it something longer term?” said Erickson. “Part of the problem is that he didn’t hold onto the 9.12 stuff and it’s kind of descended into competing factions and chaos. He is going to have to be careful, I think, to make sure that he perpetuates this in some way or it’s going to start becoming a punch line.”

Meanwhile, at least one tea party group rejected Beck’s entreaties to assist with the march, concluding he was offering little in return for its organizational know-how and credibility, while giving preferential treatment to FreedomWorks, which is paying to sponsor Beck’s radio show. The group’s leader, who requested anonymity to avoid antagonizing Beck, said, “All he’s doing is trying to use us to promote himself.”

Still other tea partiers have grumbled that Beck’s rally is a spotlight-grabbing provocation that’s detracting from a previously planned tea party rally on Sept. 12 and threatening to set back a movement that has struggled to maintain a leaderless structure and a fiscal focus, while fending off liberal charges of racism. The Rev. Al Sharpton and other civil rights leaders have planned a “Reclaim the Dream” rally in Washington to coincide with Beck’s event.

“I call it ‘Beckaplooza’ because it seems to be all about Beck,” said Andrew Dodge, the Maine state coordinator for Tea Party Patriots, a coalition of local groups that has helped stage several big rallies, including the seminal tea party rally on Sept. 12, 2009, that drew tens of thousands of people to Washington’s National Mall to protest what they saw as unchecked government expansion under President Barack Obama and the Democratic Congress.

At the request of Beck’s team, which lacked the organizational infrastructure or logistical know-how to pull off Saturday’s march, Tea Party Patriots agreed to help promote the march among its 500,000 e-mail subscribers and to provide 400 volunteers to staff it, a requirement before the National Park Service would issue a permit.

But when the Patriots were deciding whether to help with Saturday’s rally, Dodge said there was internal queasiness over the M.L.K. link and Beck’s inflammatory rhetoric, including his blasting of Obama as a racist.

“There have been discussions continuously over the last year about whether he is necessarily a force for good or not necessarily,” said Dodge, who is not planning to attend Beck’s rally and expressed concern that it could produce controversy that might haunt the tea party. “Beck takes it outside of the realm of fiscal conservatism into issues that are more emotional and make you wonder if we really want to be associated with this guy.”

Fox News has kept its distance from the rally, announcing it will not air the event, but instead will cover it as “a news event.”

Fox executive Bill Shine told POLITICO that the network doesn’t even plan to carry Palin’s speech live. And he said that though Beck has talked about the event on his Fox show, “there is no organized promotion planned for the rally on Fox News, and the network has nothing to do with it.”

Conservative groups, though, are taking advantage of potentially massive turnout — Beck recently suggested that the rally’s turnout might be rivaled only by the estimated 1.8 million who attended Obama’s inauguration — to host a number of political events around the rally.

On Sunday, the Tea Party Patriots are planning a rally urging the repeal of the Democratic health care overhaul, while on Friday night, FreedomWorks’s political action committee is holding a fundraiser and get-out-the-vote training session. And Americans for Prosperity moved its annual Washington training session to correspond with Beck’s rally and are offering to bus attendees to it.

Beck’s original idea for the rally was an overtly political event that was to have doubled as a massive launch party for a political organizing book he was writing called “The Plan,” which he billed as providing “specific policies, principles and, most importantly, action steps” to launch “a new national movement to restore our great country.” That idea, which he announced to much fanfare at a November rally in Florida during his last book tour, also included a series of pay-for-admission “conventions,” which included voter registrations and training on “how to be a political force in your own neighborhood and country.”

It was all part of what Beck suggested was a shift to a more politically active approach. But he abruptly dropped those plans — and the idea for “The Plan” — early this year, telling his radio listeners in January he quickly realized after the Florida rally that “this is the wrong direction” because it would force his followers to engage in a partisan political system he blasts as corrupt.

From a media industry perspective, if Beck draws anywhere close to 100,000 people, it would far surpass the estimated 10,000 people who flocked to a 1993 New York City book signing by shock jock Howard Stern or events held by any other talkers, said Michael Harrison, founder and publisher of Talkers Magazine, a trade publication that monitors talk media and its personalities.

“If, in fact, that many people come to an event that was created by Beck, then it will be historic in the annals of broadcasting,” said Harrison. “And then, obviously, he is more than just an entertainer. He is somebody who is able to motivate people politically.”

Beck’s ability to motivate his followers to activism was proved by his forays into tea party activism through The 9.12 Project.

Named for the day after the Sept. 11 terrorist attacks, when Beck says the nation was most unified, and for the nine principles and 12 values that Beck asserts could recreate that unity, Beck launched the project during a March 2009 edition of his Fox show.

He established a website for the project on Fox News’ server and encouraged his fans to become politically active in their communities and to attend the Sept. 12, 2009, tea party rally in Washington. The subsequent formation of dozens — if not hundreds — of local 9.12 groups, as well as the tens of thousands who turned out for the rally, where many activists credited Beck for their attendance and some waved "Beck for President" signs, proved Beck’s potential as a political force on the right.

But all the while, Beck proclaimed himself merely a supportive outside observer and protested that he was not involved in partisan politics, even as he delivered the keynote address to February’s Conservative Political Action Conference, a mainstay of Washington Republicans.

Beck’s lack of engagement led to an erosion of the ranks of 9.12 groups, which in some cases have been absorbed by tea party groups, said Erickson and Roger Boone of Flagstaff, Ariz., who briefly was involved in the 9.12 effort before organizing the Flagstaff Tea Party.

“People kind of thought that Beck would be more involved than he has been, but he just backed off for a while — I don’t know if it was his job or what,” said Boone. “I thought he would give more guidance to the groups that formed, because he basically came up with the whole idea of 9.12 — it was his baby, his creation,” said Boone, who is not going to Saturday’s rally.

Several tea party and 9.12 activists told POLITICO their groups remain active and inspired by Beck, and are sending big delegations to Saturday’s rally.

“We have about 60 people, and I would guess that 30 of them are going,” said Laura Ensor, organizer of the 9.12 group in South Carolina’s Low Country. She sees Beck’s role as more educational and inspirational than hands on.

But Beck conceded during his Fox News show late last month that 9.12 activists continue to urge him to take a more active political role, recalling an activist who approached one of his staffers “a couple weeks ago, when I was on the road, and they said, ‘Glenn's got to get involved in 9.12. We're not leaders; we don't know what we're doing, blah, blah.’ And I actually, because I was a little stressed out at the time, I said to my staff member, ‘call them up and just say, ‘Do they think I know what I'm doing?’"